Funding for this research was provided by:
National Institute for Health Research
Article History
Received: 7 April 2018
Accepted: 17 August 2018
First Online: 21 September 2018
Ethics approval and consent to participate
: Not relevant, this is a literature review with no primary research data or data from human subjects.
: No individual person’s data in any form.
: The authors declare that they have no competing interests.
: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.